I was recently regarding A Child's History of England by Charles Dickens when I came across this sentence:
However, for once that the bold Britons beat him [Julius Caesar], he beat them twice; though not so soundly but that he was very glad to accept their proposals of peace, and go away.
I don't quite understand the bolded part. Did he beat them soundly? Not so soundly? Was he glad to accept their proposals of peace or not? How does the grammar function here?